man/major.texi

   1 @c This is part of the Emacs manual.
   2 @c Copyright (C) 1985, 86, 87, 93, 94, 95, 97, 2000 Free Software Foundation, Inc.
   3 @c See file emacs.texi for copying conditions.
   4 @node Major Modes, Indentation, International, Top
   5 @chapter Major Modes
   6 @cindex major modes
   7 @cindex mode, major
   8 @kindex TAB @r{(and major modes)}
   9 @kindex DEL @r{(and major modes)}
  10 @kindex C-j @r{(and major modes)}
  11
  12   Emacs provides many alternative @dfn{major modes}, each of which
  13 customizes Emacs for editing text of a particular sort.  The major modes
  14 are mutually exclusive, and each buffer has one major mode at any time.
  15 The mode line normally shows the name of the current major mode, in
  16 parentheses (@pxref{Mode Line}).
  17
  18   The least specialized major mode is called @dfn{Fundamental mode}.
  19 This mode has no mode-specific redefinitions or variable settings, so
  20 that each Emacs command behaves in its most general manner, and each
  21 user option variable is in its default state.  For editing text of a
  22 specific type that Emacs knows about, such as Lisp code or English
  23 text, you should switch to the appropriate major mode, such as Lisp
  24 mode or Text mode.
  25
  26   Selecting a major mode changes the meanings of a few keys to become
  27 more specifically adapted to the language being edited.  The ones that
  28 are changed frequently are @key{TAB}, @key{DEL}, and @kbd{C-j}.  The
  29 prefix key @kbd{C-c} normally contains mode-specific commands.  In
  30 addition, the commands which handle comments use the mode to determine
  31 how comments are to be delimited.  Many major modes redefine the
  32 syntactical properties of characters appearing in the buffer.
  33 @xref{Syntax}.
  34
  35   The major modes fall into three major groups.  The first group
  36 contains modes for normal text, either plain or with mark-up.  It
  37 includes Text mode, HTML mode, SGML mode, @TeX{} mode and Outline
  38 mode.  The second group contains modes for specific programming
  39 languages.  These include Lisp mode (which has several variants), C
  40 mode, Fortran mode, and others.  The remaining major modes are not
  41 intended for use on users' files; they are used in buffers created for
  42 specific purposes by Emacs, such as Dired mode for buffers made by
  43 Dired (@pxref{Dired}), Mail mode for buffers made by @kbd{C-x m}
  44 (@pxref{Sending Mail}), and Shell mode for buffers used for
  45 communicating with an inferior shell process (@pxref{Interactive
  46 Shell}).
  47
  48   Most programming-language major modes specify that only blank lines
  49 separate paragraphs.  This is to make the paragraph commands useful.
  50 (@xref{Paragraphs}.)  They also cause Auto Fill mode to use the
  51 definition of @key{TAB} to indent the new lines it creates.  This is
  52 because most lines in a program are usually indented
  53 (@pxref{Indentation}).
  54
  55 @menu
  56 * Choosing Modes::     How major modes are specified or chosen.
  57 @end menu
  58
  59 @node Choosing Modes,,Major Modes,Major Modes
  60 @section How Major Modes are Chosen
  61
  62 @cindex choosing a major mode
  63   You can select a major mode explicitly for the current buffer, but
  64 most of the time Emacs determines which mode to use based on the file
  65 name or on special text in the file.
  66
  67   Explicit selection of a new major mode is done with a @kbd{M-x} command.
  68 From the name of a major mode, add @code{-mode} to get the name of a
  69 command to select that mode.  Thus, you can enter Lisp mode by executing
  70 @kbd{M-x lisp-mode}.
  71
  72 @vindex auto-mode-alist
  73   When you visit a file, Emacs usually chooses the right major mode based
  74 on the file's name.  For example, files whose names end in @samp{.c} are
  75 edited in C mode.  The correspondence between file names and major modes is
  76 controlled by the variable @code{auto-mode-alist}.  Its value is a list in
  77 which each element has this form,
  78
  79 @example
  80 (@var{regexp} . @var{mode-function})
  81 @end example
  82
  83 @noindent
  84 or this form,
  85
  86 @example
  87 (@var{regexp} @var{mode-function} @var{flag})
  88 @end example
  89
  90 @noindent
  91 For example, one element normally found in the list has the form
  92 @code{(@t{"\\.c\\'"} . c-mode)}, and it is responsible for selecting C
  93 mode for files whose names end in @file{.c}.  (Note that @samp{\\} is
  94 needed in Lisp syntax to include a @samp{\} in the string, which must
  95 be used to suppress the special meaning of @samp{.} in regexps.)  If
  96 the element has the form @code{(@var{regexp} @var{mode-function}
  97 @var{flag})} and @var{flag} is non-@code{nil}, then after calling
  98 @var{mode-function}, Emacs discards the suffix that matched
  99 @var{regexp} and searches the list again for another match.
 100
 101 @vindex magic-mode-alist
 102   Sometimes the major mode is determined from the way the file's text
 103 begins.  The variable @code{magic-mode-alist} controls this.  Its value
 104 is a list of elements of this form:
 105
 106 @example
 107 (@var{regexp} . @var{mode-function})
 108 @end example
 109
 110 @noindent
 111 This looks like an element of @code{auto-mode-alist}, but it doesn't work
 112 the same: this @var{regexp} is matched against the text at the start
 113 of the buffer, not against the file name.  @code{magic-mode-alist}
 114 takes priority over @code{auto-mode-alist}.
 115
 116   You can specify the major mode to use for editing a certain file by
 117 special text in the first nonblank line of the file.  The
 118 mode name should appear in this line both preceded and followed by
 119 @samp{-*-}.  Other text may appear on the line as well.  For example,
 120
 121 @example
 122 ;-*-Lisp-*-
 123 @end example
 124
 125 @noindent
 126 tells Emacs to use Lisp mode.  Such an explicit specification overrides
 127 any defaults based on the file name.  Note how the semicolon is used
 128 to make Lisp treat this line as a comment.
 129
 130   Another format of mode specification is
 131
 132 @example
 133 -*- mode: @var{modename};-*-
 134 @end example
 135
 136 @noindent
 137 which allows you to specify local variables as well, like this:
 138
 139 @example
 140 -*- mode: @var{modename}; @var{var}: @var{value}; @dots{} -*-
 141 @end example
 142
 143 @noindent
 144 @xref{File Variables}, for more information about this.
 145
 146 @vindex interpreter-mode-alist
 147   When a file's contents begin with @samp{#!}, it can serve as an
 148 executable shell command, which works by running an interpreter named on
 149 the file's first line.  The rest of the file is used as input to the
 150 interpreter.
 151
 152   When you visit such a file in Emacs, if the file's name does not
 153 specify a major mode, Emacs uses the interpreter name on the first line
 154 to choose a mode.  If the first line is the name of a recognized
 155 interpreter program, such as @samp{perl} or @samp{tcl}, Emacs uses a
 156 mode appropriate for programs for that interpreter.  The variable
 157 @code{interpreter-mode-alist} specifies the correspondence between
 158 interpreter program names and major modes.
 159
 160   When the first line starts with @samp{#!}, you cannot (on many
 161 systems) use the @samp{-*-} feature on the first line, because the
 162 system would get confused when running the interpreter.  So Emacs looks
 163 for @samp{-*-} on the second line in such files as well as on the
 164 first line.
 165
 166 @vindex default-major-mode
 167   When you visit a file that does not specify a major mode to use, or
 168 when you create a new buffer with @kbd{C-x b}, the variable
 169 @code{default-major-mode} specifies which major mode to use.  Normally
 170 its value is the symbol @code{fundamental-mode}, which specifies
 171 Fundamental mode.  If @code{default-major-mode} is @code{nil}, the major
 172 mode is taken from the previously current buffer.
 173
 174 @findex normal-mode
 175   If you change the major mode of a buffer, you can go back to the major
 176 mode Emacs would choose automatically: use the command @kbd{M-x
 177 normal-mode} to do this.  This is the same function that
 178 @code{find-file} calls to choose the major mode.  It also processes
 179 the file's @samp{-*-} line or local variables list (if any).
 180 @xref{File Variables}.
 181
 182 @vindex change-major-mode-with-file-name
 183   The commands @kbd{C-x C-w} and @code{set-visited-file-name} change to
 184 a new major mode if the new file name implies a mode (@pxref{Saving}).
 185 (@kbd{C-x C-s} does this too, if the buffer wasn't visiting a file.)
 186 However, this does not happen if the buffer contents specify a major
 187 mode, and certain ``special'' major modes do not allow the mode to
 188 change.  You can turn off this mode-changing feature by setting
 189 @code{change-major-mode-with-file-name} to @code{nil}.
 190
 191 @ignore
 192    arch-tag: f2558800-cf32-4839-8acb-7d3b4df2a155
 193 @end ignore